Circuit arrangement for operating a gas sensor

Abstract

A circuit configuration for operating a gas sensor is described, including a reference gas space in which an electrode is situated which is supplied with a reference gas pump current to maintain the concentration of the reference gas. A diagnostic system determines a concentration change of the reference gas via a change in the reference pump current and a time-based evaluation of the sensor signal of the gas sensor.

1. A circuit configuration for operating a gas sensor, comprising:
 a structure including a reference gas space; 
 a reference electrode situated in the reference gas space; 
 a current source for supplying a reference pump current to the reference electrode; and 
 a diagnostic system including a timer, wherein the diagnostic system:
 delivers a current selection signal to the current source for setting the reference pump current during a diagnostic operation of the gas sensor; 
 delivers a switch signal to the timer for starting the timer; 
 evaluates a sensor signal of the gas sensor during diagnostic operation based on time; and 
 evaluates a rate of change of the sensor signal. 
 
 
   
   
     2. The circuit configuration as recited in  claim 1 , wherein the diagnostic system includes a comparator that compares the sensor signal with a threshold value to produce a comparison result and supplies a diagnostic signal as a function of the comparison result. 
   
   
     3. The circuit configuration as recited in  claim 2 , wherein the diagnostic signal stops the timer. 
   
   
     4. The circuit configuration as recited in  claim 1 , further comprising:
 a resistor, wherein:
 the reference electrode is permanently connected to a predefined potential across the resistor, and 
 a discharge current flowing across the resistor pumps out a reference gas. 
 
 
   
   
     5. The circuit configuration as recited in  claim 1 , wherein the gas sensor is a lambda sensor and the reference gas space contains oxygen as a reference gas. 
   
   
     6. The circuit configuration as recited in  claim 5 ,
 wherein the lambda sensor is situated in an exhaust gas system of an internal combustion engine and an enable signal triggers the diagnosis after shutdown of the internal combustion engine. 
 
   
   
     7. A circuit configuration for operating a gas sensor, comprising:
 a structure including a reference gas space; 
 a reference electrode situated in the reference gas space; 
 a current source for supplying a reference pump current to the reference electrode; and 
 a diagnostic system including a timer, wherein:
 the diagnostic system delivers a current selection signal to the current source for setting the reference pump current during a diagnostic operation of the gas sensor; 
 the diagnostic system delivers a switch signal to the timer for starting the timer; 
 the diagnostic system evaluates a sensor signal of the gas sensor during diagnostic operation based on time; 
 the diagnostic system includes a comparator that compares the sensor signal with a threshold value to produce a comparison result and supplies a diagnostic signal as a function of the comparison result; 
 the diagnostic signal stops the timer; 
 the timer supplies an end signal that represents a time elapsed, and 
 the current selection signal is set as a function of the end signal for operating the gas sensor outside of the diagnostic operation. 
 
 
   
   
     8. The circuit configuration as recited in  claim 7 , wherein a time determinable by the timer is set at a maximum time. 
   
   
     9. The circuit configuration as recited in  claim 7 , wherein the current selection signal one of triggers the current source to supply a negative reference pump current and shuts down the current source. 
   
   
     10. The circuit configuration as recited in  claim 7 , further comprising:
 a resistor, wherein:
 the reference electrode is permanently connected to a predefined potential across the resistor, and 
 a discharge current flowing across the resistor pumps out a reference gas. 
 
 
   
   
     11. The circuit configuration as recited in  claim 7 , wherein the gas sensor is a lambda sensor and the reference gas space contains oxygen as a reference gas. 
   
   
     12. The circuit configuration as recited in  claim 11 ,
 wherein the lambda sensor is situated in an exhaust gas system of an internal combustion engine and an enable signal triggers the diagnosis after shutdown of the internal combustion engine.